Method for mapping layer-3 packets over SDH/SONET or OTN via GFP layer

ABSTRACT

The present invention provides for a method for mapping MPLS packets over Synchronous Digital Transport Networks (SDH/SONET) or Optical Transport Networks (OTN) via GFP mapping layer, through a modified PPP protocol without the LCP and NCP protocols for negotiation. In the modified PPP protocol the MPLS or IP packets are inserted, and then the GFP header is added. In order to map the modified PPP over GFP a new UPI (User Paylod Identifier) value is defined in the GFP Core header.

TECHNICAL FIELD

[0001] The present invention relates to a method for mapping layer-3packets over Synchronous Digital Transport Networks (SDH/SONET) orOptical Transport Networks (OTN) via GFP mapping layer.

[0002] This application is based on, and claims the benefit of, EuropeanPatent Application No. 03290790.9 filed on Mar. 28, 2003 which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

[0003] As known, MPLS is an example of network layer 3 protocol definedby IETF body in the standard RFC 3031.

[0004] According to this definition, in order to transport MPLS packetsover a point-to-point (layer 1) Synchronous Digital Transport Network(SDH/SONET) or Optical Transport Network (OTN) path, a layer 2 protocolshould be used.

[0005] The known PPP (Point-to-point) protocol has been selected by IETFbody for MPLS transport over point-to-point lines, as described in thestandard RFC 3032.

[0006] The main functionality PPP provides is “protocol multiplexing”:it allows multiple protocols above layer 2 to share the samepoint-to-point connection.

[0007] As also known, GFP (Generic Frame Procedure) is a mapping layerof layer 2 frames over a layer 1 SDH/SONET/OTN transport path, ascurrently defined in the standard ITU-T G.7041.

[0008] GFP does not provide protocol multiplexing functionality, as PPPdoes, and then it violates the architectural principles used in IETFwhen MPLS has been defined. MPLS packets can anyway be sent over GFPpassing through the PPP layer.

[0009] According to ITU-T G.7041, PPP frames (encapsulating the MPLSpacket or any other layer 3 packet) can be mapped into GFP and then intothe SDH/SONET/OTN transport path.

[0010] Alternatively, according to IETF RFC 2615, RFC 1661 and RFC 1662,the same PPP frames can be mapped via HDLC (High level Data LinkController) mapping layer into the SDH/SONET transport path (Packet overSonet).

[0011] Therefore, according to the current IETF and ITU-T standards,there are two possible methods for carrying MPLS packets over SDH/SONETtransport path.

[0012] Both solutions require MPLS over PPP (according to RFC 3032) andthen there are two alternatives for mapping PPP over SDH/SONET transportpath:

[0013] 1. PPP over HDLC-like framing (RFC 1661, RFC 1662, RFC 2615)

[0014] 2. PPP over GFP (ITU-T G.7041): this solution allows also themapping over OTN.

[0015] In both cases the standard PPP solution requires to run the knownprotocol LCP (Link Control Protocol) according to RFC 1661 and RFC 1662,and at least the protocol MPLSCP (MPLS Network Control Protocol—NCP)according to RFC 1661 and RFC 3032. They are mainly required forinterworking because of standard PPP requirements, primarily in“dynamic” connection environments, like “private dial-up” connection,where it is necessary to negotiate the network/traffic resources beforeconnection set-up. The traffic is stopped till the end of thenegotiation phase.

[0016] However, the running of LCP and NCP is not really needed when thepoint-to-point link is supported by an SDH/SONET/OTN transport path,where there is no need for negotiation as the connection is “static”like: in these conditions the running of LCP and NCP should introduceinefficiencies in the network throughput.

SUMMARY OF THE INVENTION

[0017] Therefore the main object of the present invention is to providea method for mapping layer-3 packets over Synchronous Digital TransportNetworks (SDH/SONET) or Optical Transport Networks (OTN) via GFP mappinglayer, which overcomes the above mentioned drawbacks.

[0018] This object is achieved by a method for mapping layer-3 packetsover Synchronous Digital Transport Networks (SDH/SONET) and/or OpticalTransport Networks (OTN), said method comprising the steps of:

[0019] setting up SDH/SONET and/or OTN connections over respectivenetworks;

[0020] setting up a modified PPP protocol of PPP packets, without theLCP and NCP protocols for negotiation;

[0021] inserting the layer-3 packets in the modified PPP packet;

[0022] adding a GFP header of a GFP mapping layer to the the modifiedPPP packet, to get GFP packets;

[0023] setting a new value of UPI (User Paylod Identifier) field in theGFP header;

[0024] transmitting GFP packets so obtained over the SDH/SONET and/orOTN networks.

[0025] The basic idea of the present invention is to propose a modifiedPPP protocol without the LCP and NCP protocols for negotiation, to bepreferably but not exclusively used in all application where negotiationis not required.

[0026] In the PPP protocol the layer-3 packets (like MPLS or IP) areinserted, and then the GFP header is added.

[0027] In order to map this new PPP over GFP it is required to define anew UPI (User Paylod Identifier) value in the GFP Core header (ITU-T G.7041).

BEST MODE OF CARRYING OUT THE INVENTION

[0028] The invention will become clear from the following detaileddescription, given by way of a mere exemplifying and non limitingexample, to be read with reference to the attached drawing FIG. 1,wherein the packet structure according to the invention is shown.

[0029] The preferred situation where the present invention applies isthe point-to-point connection transmission system using SynchronousDigital Transport Networks (SDH/SONET) or Optical Transport Networks(OTN), made of a number of interconnected nodes.

[0030] The target is to map layer-3 MPLS or IP packets over SDH/SONET orOTN networks via GFP mapping layer, in such a way as to avoid theactivation of the LCP and NCP negotiation protocols.

[0031] The basic idea of the present invention is to propose a modifiedPPP protocol without the LCP and NCP protocols for negotiation, to bepreferably but not exclusively used in all applications wherenegotiation is not required. In the modified PPP protocol the MPLS or IPpackets are inserted, and then the GFP header is added.

[0032] The point-to-point connections between nodes are establishedaccording to the known SDH/SONET or OTN criteria.

[0033] At the nodes the properties and parameters of the modified PPPprotocol are configured, as well as the network protocol (IP address)through the Network Management system TMN of the SDH/SONET or OTNnetworks.

[0034] Then at the nodes the fields of the GFP layer are inserted.

[0035] The packets so obtained are transmitted over SDH/SONET or OTNnetworks in a known way.

[0036] The various fields of the overall packet are shown in FIG. 1.

[0037] A layer-3 packet, like MPLS or IP, is encapsulated into themodified PPP layer, having:

[0038] a PPP header, field Protocol, the value of which identifies thetype of payload: this can be any of the layer 3, i.e. MPLS or IP or IPXor IPv6;

[0039] the said payload, i.e. an MPLS or IP packet comprising in turn anheader and a payload part;

[0040] a PPP tail, field FCS, used for error checking of the PPP packet.

[0041] Then the GFP header is built up with the following fields:

[0042] PLI: payload length indication;

[0043] HEC: Header Error Check, with the following possibilities:

[0044] cHEC: core HEC, check on the Header field;

[0045] tHEC: type HEC, check on the Type field;

[0046] eHEC: extension HEC, check on the Extension header;

[0047] PTI: Payload Type identifier;

[0048] PFI: Payload FCS identifier;

[0049] EXI: Extension Header identifier;

[0050] UPI: User Payload identifier: in order to map the new PPP overGFP it is required to define a new UPI (User Paylod Identifier) value inthe GFP Core header (ITU-T G. 7041), which identifies the new kind ofPPP packet.

[0051] Normally the fields PFI and EXI are put at Ø.

[0052] With a different value of EXI field it is possible to add anextension header to the basic GFP: this should allow for example to putmore than one different GFP channels in the same SDH/SONET VirtualContainer.

[0053] With PFI=1, it is possible to add an FCS field of the GFP levelat the bottom of the overall packet; in the normal situation this is notnecessary, as an FCS field of the PPP level is already present.

[0054] Another possibility is to set EXI field at a given differentvalue; then to set the UPI field at a different value with respect toabove. This should allow to consider that the value of protocol type hasto be read in the GFP Extension Header. Then an HEC field is put in theGFP extension header, and the layer 3 packet is inserted, and at thebottom an GFP FCS field. With PFI=1, the result is that the PPP layer ishidden in the GFP layer.

[0055] With the above described procedure, the activation of the LCP andNCP negotiation protocols is not necessary.

[0056] Further implementation details will not be described, as the manskilled in the art is able to carry out the invention starting from theteaching of the above description.

[0057] From the above description, the advantages of the presentinvention are clear, namely:

[0058] To avoid the usage of negotiating protocols when not necessary.

[0059] Robust solution because GFP based.

[0060] Valid for both Sonet/SDH and OTN

[0061] Standard compliant for interoperability purpose.

[0062] Many changes, modifications, variations and other uses andapplications of the subject invention will become apparent to thoseskilled in the art after considering the specification and theaccompanying drawings which disclose preferred embodiments thereof. Allsuch changes, modifications, variations and other uses and applicationswhich do not depart from the spirit and scope of the invention aredeemed to be covered by this invention.

1. Method for mapping layer-3 packets over Synchronous Digital TransportNetworks (SDH/SONET) and/or Optical Transport Networks (OTN), saidmethod comprising the steps of: setting up SDH/SONET and/or OTNconnections over respective networks; setting up a modified PPP protocolof PPP packets, without the LCP and NCP protocols for negotiation;inserting the layer-3 packets in the modified PPP packet; adding a GFPheader of a GFP mapping layer to the the modified PPP packet, to get GFPpackets; setting a new value of UPI (User Paylod Identifier) field inthe GFP header; transmitting GFP packets so obtained over the SDH/SONETand/or OTN networks.
 2. Method according to claim 1, wherein saidmodified PPP protocol of PPP packets comprises: a PPP header, fieldProtocol, the value of which identifies the type of layer-3 payload; thesaid layer-3 payload, comprising in turn an header and a payload part; aPPP tail, field FCS, used for error checking of the PPP packet. 3.Method according to claim 1, wherein said layer-3 packets are MPLS or IPor IPX or IPv6.
 4. Method according to claim 1, wherein said GFP headercomprises the following fields: PLI: payload length indication; HEC:Header Error Check, with the following possibilities: cHEC: core HEC,check on the Header field; tHEC: type HEC, check on the Type field;eHEC: extension HEC, check on the Extension header; PTI: Payload Typeidentifier; PFI: Payload FCS identifier; EXI: Extension Headeridentifier; UPI: User Payload identifier: the said new value of UPI.